Strip Surcharge - Active Earth Pressure

For vertical strip load fa acting parallel with structure on the ground surface along an infinitely long strip the trapezoidal increment of active earth pressure applied to the structure over a given segment hf is assumed - see figure.

Diagram of increment of active earth pressure due to strip load fa

This segment is determined by intersection of the structure and lines drawn from the edge points of the strip load having slopes associated with angles φ and ϑa. The angle ϑa corresponding to critical slip plane follows from:

The formula is described in more detail in section "Active earth pressure - line surcharge".

Variation of pressure increment is trapezoidal; the larger intensity of Δσfs is applied at the upper end while the smaller intensity of Δσfi at the bottom end. The two increments are given by:

where:

fa

-

magnitude of strip surcharge

b

-

width of the strip surcharge acting normal to the structure

hf

-

section loaded by active earth pressure increment

where:

ϑa

-

angle of critical slip plane

φ

-

angle of internal friction of soil

δ

-

angle of friction between structure and soil

The resultant of the increment of active earth pressure due to strip load fa is provided by: